High performance cannulas

ABSTRACT

A cannula having a proximal end, a distal end, and a lumen extending between the proximal and distal ends is provided. The diameter of the lumen of the cannula can be varied to take into account differences in the diameter of access and target vessels during cannulation. The cannula is further characterized by at least one mechanism that, upon actuation, serves to alter the conformation of the cannula between a normal profile conformation and a low profile conformation. The normal profile conformation is characterized by the cannula having a lumen diameter at the point of insertion, which is smaller than the lumen diameter both proximal and distal to the point of insertion, with the lumen diameter distal to the point of insertion also expandable to the diameter of the cannulated vessel of the patient. The low profile conformation is characterized by the cannula having a lumen diameter at the point of insertion that is greater than the lumen diameter distal to the point of insertion.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/484,673, filed Jul. 7, 2003, which is herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

The invention relates to cannulas and, more particularly, to highperformance cannulas, where the diameter of the lumen of the cannula canbe varied.

BACKGROUND OF THE INVENTION

Cannulas are used in a wide variety of applications. For example,cannula assemblies are typically used in minimally invasive surgicalprocedures including laparoscopic, endoscopic, and arthroscopicprocedures. Cannulas can also be used to deploy operatinginstrumentation during such minimally invasive procedures. Additionally,during coronary surgery, venous and arterial cannulas are used toconduct blood between the body and the bypass equipment. Moreover,cannulas are also used as vents, as sumps, and for chest tube fluidsuction. Cannulas can also be used in a variety of non-medical contexts.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a cannula adapted for insertionat a point of insertion. The cannula includes a cannula body having aproximal end, a distal end, and a lumen extending between the proximaland distal ends. The lumen has a diameter and the cannula body includesa plurality of flexible filaments that allow the diameter of the lumento be varied. The distal end optionally further comprises a tip, whichcan be removable or eccentrically located. The cannula also includes atleast one mechanism that, upon actuation, serves to alter theconformation of the cannula between a normal profile conformation and alow profile conformation. For example, the mechanism is selected from amandrel, an electric motor, a change in pressurization, a wrappingstring, a balloon and a sheath. When the cannula is in use, the normalprofile conformation is characterized by the cannula having a lumendiameter at the point of insertion, which is smaller than the lumendiameter both proximal and distal to the point of insertion. The lumendiameter distal to the point of insertion is expandable up to thediameter of a surrounding vessel or up to the maximum lumen diameter.The low profile conformation is characterized by the cannula having alumen diameter at the point of insertion that is greater than the lumendiameter distal to the point of insertion.

The plurality of flexible filaments may include one or more materialsselected from metals, shape-memory metals, alloys, plastics, textilefibers, synthetic fibers, and/or combinations thereof. For example, themetal can be stainless steel. Moreover, the plurality of flexiblefilaments can have a shape selected from round, oval, flattened,triangular, rectangular and combinations thereof. In one embodiment, theplurality of flexible filaments are textile fibers.

Those skilled in the art will recognize that the plurality of flexiblefilaments can be braided together, knitted together or interwoven.Alternatively, the plurality of flexible filaments are interlaced.

The cannula is designed to be inserted into hollow organ, which can beselected from, for example, a vein, an artery, a urethra, a ureter, anintestine, an esophagus, a trachea, a bronchial tube, a pleural space,and/or a peritoneum.

When the cannula is in its normal profile conformation when in use, thelumen diameter distal to the point of insertion varies in relation tothe diameter of the surrounding vessel. Further, the cannula is in itsnormal profile conformation when in use, the portion of the cannuladistal to the point of insertion supports an inner surface of thesurrounding vessel.

The plurality of flexible filaments may be elastic and/or plastic innature. The cannula may be coated with a watertight coating, which canbe a plastic, such as, for example, silicone. The cannula tip may bepotted using a material such as a photoactivated epoxy. The cannula mayfurther include a connecting sleeve to couple the cannula to a device.

The flow rate of fluid through the cannulas of the invention can be lessthan about 150 mL/min. In some of the cannulas, the flow rate of fluidthrough the cannula is between about 1 mL/min and about 10 mL/min.

The invention provides methods for using the cannula in medicalcontexts. Such methods include placing the cannula in its low profileconformation, inserting the cannula into a hollow organ of a patient ata point of insertion, and returning the cannula to its normal profileconformation. In the normal profile conformation, the cannula expandsdistal to the point of insertion up to the diameter of the hollow organor up to the maximum diameter of the lumen.

For example, when the cannula is in the normal profile conformation, thediameter of the cannula distal to the point of insertion varies inrelation to the diameter of the hollow organ. Inserting the cannula intothe hollow organ of the patient can include inserting the cannula into alocation selected from the peritoneum, the trachea, the chest, thecardiovascular system, the kidneys, and the urinary system. For example,the hollow organ can be selected from a vein, an artery, a urethra, aureter, an intestine, an esophagus, a trachea, a bronchial tube, apleural space, and a peritoneum. In one specific embodiment, the cannulais inserted into the trachea, and the cannula can be insertedtransorally, transnasally, or through a tracheotomy.

When the cannula is used during cardiac surgery, the cannula may have aflow rate of fluid through the cannula of between about 100 mL/min and 6L/min. When used during dialysis or hemofiltration, the cannula may havea flow rate of fluid through the cannula between about 100 mL/min and500 mL/min. When used for the intravenous delivery of fluids, thecannula may have a flow rate between about 1 mL/min and about 10 mL/min.

The invention also provides methods for using the cannula in non-medicalcontexts. Such methods include placing the cannula in its low profileconformation; inserting the cannula into an object to be cannulatedselected from the group consisting of tubing, a container, afluid-filled container, a powder-filled container, and a gas-filledcontainer; and returning the cannula to its normal profile conformation.In the normal profile conformation, the cannula expands distal to thepoint of insertion up to the diameter of the object or up to the maximumlumen diameter.

Also provided are dual lumen cannula adapted for insertion at a point ofinsertion for use in, for example, peritoneal dialysis, hemodialysis orhemofiltration. Such dual lumen cannulas include a first cannula bodyhaving a proximal end, a distal end, and a lumen extending between theproximal and distal ends, and a second cannula body having a proximalend, a distal end, and a lumen extending between the proximal and distalends, the lumen of the first and second cannula bodies having adiameter. The first and second cannula bodies each include a pluralityof flexible filaments that allow the diameter of the first and secondlumen to be varied. The first and second distal ends may optionallyfurther include a tip, which is removable or eccentrically located. Thedual lumen cannula includes at least one mechanism that, upon actuation,serves to alter the conformation of the first cannula body, the secondcannula body, or both the first cannula body and the second cannulabody, between a normal profile conformation and a low profileconformation.

When the dual lumen cannula is in use, the normal profile conformationis characterized by the first and second cannula bodies having a lumendiameter at the point of insertion, which is smaller than the lumendiameter both proximal and distal to the point of insertion. The lumendiameters of the first and second cannula bodies distal to the point ofinsertion are expandable up to the diameter of a surrounding vessel orup to the maximum lumen diameter. The low profile conformation ischaracterized by the first and second cannula bodies having a lumendiameter at the point of insertion that is greater than the lumendiameter distal to the point of insertion.

The flexible filaments that make up the cannula body of the dual lumencannula may include one or more materials selected from metals,shape-memory metals, alloys, plastics, textile fibers, synthetic fibers,and/or combinations thereof. Moreover, the at least one mechanism isselected from a mandrel, an electric motor, a change in pressurization,a wrapping string, a balloon and/or a sheath. The first and secondcannula bodies of the dual lumen cannula can be positioned coaxially oradjacently.

The invention also provides methods for manufacturing the cannulaaccording to the invention. For example, the cannula can be made byinjection molding, laser-cutting, water-cutting, extrusion andcombinations thereof.

The above description sets forth rather broadly the more importantfeatures of the present invention in order that the detailed descriptionthereof that follows may be understood, and in order that the presentcontributions to the art may be better appreciated. Other objects andfeatures of the present invention will become apparent from thefollowing detailed description considered in conjunction with theexamples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cannula according to one embodiment of theinvention in its normal profile conformation. Cannulas according to thisembodiment can be used, for example, in open heart and open chestsurgical procedures.

FIG. 1B illustrates a cannula according to one embodiment of theinvention in its low profile conformation.

FIG. 1C illustrates a cannula according to one embodiment of theinvention.

FIG. 2A is a perspective view showing a view of a cannula according toone embodiment of the invention in a normal profile conformation whenthe cannula is in use according to the methods of the invention.

FIG. 2B is a perspective view showing a view of a cannula according toone embodiment of the invention in a low profile conformation.

FIG. 3A is a computer-generated drawing showing the high performancecannula according to one embodiment of the invention stretched on amandrel.

FIG. 3B is a computer-generated drawing showing the high performancecannula according to one embodiment of the invention after removal ofthe mandrel.

FIG. 4 is a diagram of a prototype high performance cannula according toone embodiment of the invention.

FIG. 5A illustrates a locking mechanism suitable for use with the highperformance cannulas of the invention.

FIG. 5B illustrates one view of a locking mechanism for use with thehigh performance cannulas of the invention.

FIG. 5C illustrates another view of a locking mechanism for use with thehigh performance cannulas of the invention.

FIG. 6A illustrates a cannula according to one embodiment of theinvention where the mechanism for altering the diameter of the cannulalumen is a sheath. In this figure, the sheath is positioned around thecannula body, thereby placing the cannula in the low profileconformation.

FIG. 6B illustrates a cannula according to the embodiment of FIG. 7A,where the sheath is partially withdrawn from the cannula.

FIG. 6C illustrates a cannula according to the embodiment of FIG. 7A,where the sheath is fully withdrawn from the cannula, and the cannula isin the normal profile conformation.

FIG. 7A illustrates a cannula according to one embodiment of theinvention where the mechanism for altering the diameter of the cannulalumen is a wrapping string. In this figure, the wrapping string ispositioned around the cannula body, thereby placing the cannula in thelow profile conformation.

FIG. 7B illustrates a cannula according to the embodiment of FIG. 8A,where the wrapping string is partially withdrawn from the cannula.

FIG. 7C illustrates a cannula according to the embodiment of FIG. 8A,where the wrapping string is fully withdrawn from the cannula, and thecannula is in the normal profile conformation.

FIG. 8A illustrates a cannula according to one embodiment of theinvention where the mechanism for altering the diameter of the cannulalumen is a balloon. In this figure, the cannula is in its low profileconformation.

FIG. 8B illustrates a cannula according to the embodiment of FIG. 9A,where the balloon returned the cannula to its normal profileconformation.

FIG. 9 illustrates a dual lumen cannula according to one embodiment ofthe present invention.

FIG. 10 provides a transparent view of the dual lumen cannula shown inFIG. 10.

FIG. 11 illustrates the cannula of FIG. 10 in its normal profileconformation after insertion into the vasculature.

FIG. 12 is a histogram showing the results of in vivo comparisonexperiments measuring the flow rates through various commerciallyavailable cannulas and the high performance cannulas of the invention.

DETAILED DESCRIPTION OF THE INVENTION

High Performance Cannulas

Minimally invasive open-heart surgery presents new problems andchallenges, some of which are due to the inadequate design oftraditional cannulas. In such cannulas, the external diameter ofcannulas to be used in target blood vessels is determined by theinternal diameter of the access vessel, which is usually smaller thanthat of the target vessel. For example, in peripheral cannulation, thediameter of the access vessel (e.g. the femoral vein) is significantlysmaller than the diameter of the target vessel (e.g. the vena cava). Asa result of this difference in diameters, relatively high cannulagradients can occur. Therefore, during peripheral cannulation, venousreturn is poor and must be augmented with vacuums or pumps. Moreover,during minimally invasive open-heart surgery, the tip of the venouscannulas cannot be placed in the right atrium of the heart, which isopen by definition. Thus, it can be impossible to reach target flowrates despite this augmentation of the venous return, because the floppycaval veins collapse and obstruct the orifices of the cannula. Whileprevious cannulas have provided expandable scaffolding, the expandablescaffolding of those cannulas acts to provide support for thesurrounding vasculature and do not allow the luminal diameter of thecannula to be varied. See, e.g., U.S. Pat. No. 6,673,042.

Those skilled in the art will recognize that a short segment of a tubeor vessel having a narrow internal diameter will not impede flow throughthe tube or vessel. In contrast, a long portion of a tube or vesselhaving a small or narrow diameter will impede flow through the object.Specifically, the segment having narrow internal diameter may constitutebetween 0% and 50% of the total length of the object. The skilledartisan will also recognize that, in a clinical setting, coronary arterystenoses of less than 50% of the diameter of the artery are notconsidered significant, and, thus, are not operated on. By “coronaryartery stenoses” is meant any stricture or narrowing of a coronaryartery.

Based on these principles and observations, a cannula having a narrowdiameter only where absolutely necessary would be expected to have muchbetter flow rate characteristics than a cannula having a narrow diameterover most of its length. Thus, the cannulas according to the presentinvention may have a small diameter only at the point of insertion.Preferably, the narrow diameter of the cannula occurs over less than 50%of the total length of the cannula, more preferably, less than 40%, morepreferably less than 30%, more preferably less than 20%, and mostpreferably, less than 10%. By “point of insertion” is meant the locationwhere the cannula is inserted into the object to be cannulated. Examplesof suitable points of insertion include, but are not limited to,arterial walls; venous walls; the skin; an orifice; the exterior oftubes and containers; and a fixed aperture on a tank or container.

Because of the narrow diameter of the cannula at the point of insertion,the access aperture of the cannula will be small. By “access aperture”is meant the hole that allows the cannula to access the object or vesselto be cannulated, i.e., the hole at the point of insertion.

Those skilled in the relevant arts will recognize that cannulation isnot limited to medical contexts. For example, non-medical uses for thehigh performance cannulas of the invention include, but are not limitedto, any situation where a continuous fluid flow and a small accessaperture is desired. Examples of non-medical uses of the highperformance cannulas according to the invention include, but are notlimited to, methods for repairing ruptured pipe, hose, or tubing where acontinuous fluid flow and a small access aperture are needed withouthaving to replace the entire length of ruptured pipe, hose, or tubing.Other examples of non-medical uses include filling or draining liquidsor liquid-like materials from any reservoir, such as a tank, pipe orcavern.

Likewise, the cannulas according to the invention can be used aspreviously described in the art. For example, see U.S. Pat. Nos.6,102,894; 6,096,012; 6,072,154; 6,036,711; 5,976,114; and 5,817,071,each of which is incorporated herein by reference.

When used in a medical context, the cannulas according to this inventioncan take advantage of the geometry of an individual's vascular tree.Specifically, cannulas according to this invention are able tocompensate for the differences in diameter between access vessels(typically smaller in diameter) and target vessels (typically larger indiameter). To compensate for these differences in diameter, the diameterof the lumen of the high performance cannula is adjustable before,during and after cannulation (i.e., insertion). Specifically, aftercannulation the diameter of the cannula either expands to that of thesurrounding vessel or environment or returns to its normal profileconformation. In contrast, traditional cannulas are limited by thediameter of the access vessel.

Cannulas according to the invention can include a cannula body having aproximal end, a distal end, and a lumen extending between the proximaland distal ends. The lumen has a diameter, and the cannula is made of aflexible material that allows the diameter of the lumen to be varied.Such cannulas also include means for altering the conformation of thecannula between a normal profile conformation and a low profileconformation, wherein the normal profile conformation is characterizedby the cannula having a lumen diameter at the point of insertion andwherein the low profile conformation is characterized by the cannulahaving a lumen diameter at the point of insertion that is greater thanthe lumen diameter distal to the point of insertion. Followingcannulation, the lumen diameter distal to the point of insertion isexpandable to the diameter of the cannulated vessel or to the normalprofile conformation diameter of the lumen.

The diameter of the lumen can be varied by altering the cannula betweena low profile conformation and a normal profile conformation. By “normalprofile conformation” is meant any conformation similar to that shown inFIG. 1A or 2A. According to one embodiment, and as illustrated in FIG.2A, for example, when the cannula 6 is in use, the normal profileconformation may be characterized by the cannula 6 having a lumendiameter 5 at the point of insertion 2, which is smaller than the lumendiameter 5 both proximal and distal to the point of insertion 2 (e.g.,the diameter of the surrounding vessel). Alternatively, as shown in FIG.1A, the cannula 6 in a normal profile conformation following cannulationcan have the shape and diameter of the lumen 5 of the cannula 6 prior tocannulation. In either normal profile conformation, the cannula 6 ischaracterized by a larger diameter of the lumen 5 as compared to thediameter of the lumen 5 when the cannula is in the low profileconformation.

By “low profile conformation” is meant any conformation similar to thatshown in FIG. 2B. According to one embodiment, illustrated in FIG. 2B,for example, the low profile conformation may be characterized by thecannula having a lumen diameter 5 at the point of insertion 2 that isgreater than the lumen diameter 5 distal to the point of insertion 2. Inits low profile conformation, a portion of the cannula 6 ischaracterized by a narrow diameter of the lumen 5 that is suitable forinsertion into the object to be cannulated as well as into smalleraccess vessels. Placing the cannula in the low profile conformation ofthe cannula 6 can be achieved by the deformation of a shape memorymetal, the deformation of an elastic, bendable, moldable, or flexiblematerial; the activation of one or more diameter-varying mechanisms; andthe deactivation of one or more diameter-varying mechanisms. One skilledin the relevant art will also recognize that placing the cannula in thelow profile conformation can be done before, during, and/or aftercannulation.

With any of the cannulas of the invention, in the normal profileconformation, the diameter of the lumen 5 at the point of insertion 2can be narrower than the diameter at the proximal end 1 and/or thedistal end 3. The diameter of the lumen 5 at the proximal end 1 and thedistal end 3 may be the same or different. Typically, the diameter ofthe lumen 5 at the distal end 3 is greater than the diameter of thelumen 5 at the point of insertion 2. The diameter of the lumen 5 distalto the point of insertion 2 is either the same as the diameter proximalto the point of insertion 2 (i.e., the diameter of the lumen 5, in thenormal profile conformation) or it expands to that of the surroundingvessel or environment.

By “proximal” is meant the external end of the cannula 6 that is notinserted into the object or vessel to be cannulated. Similarly, by“distal” is meant the end of the cannula 6 that is inserted into theobject or vessel to be cannulated.

Turning now to the drawings, and to FIGS. 1-4 and 7-9 in particular,various embodiments of the cannula 6 according to the invention isshown. These cannulas 6 comprise a cannula body 4 having a proximal end1, a distal end 3, and a lumen 5 having an internal diameter thatextends between the proximal end 1 and the distal end 3.

In one embodiment, the cannula 6 is made of a flexible, deformable ormoldable material that can be altered to allow the diameter of the lumen5 to be varied. By “diameter of the lumen” is meant the diameter of thelumen 5 of the cannula body 4.

For example, the cannula body 4 may be made out of a plurality offlexible filaments that allows the diameter of the lumen 5 to be varied.The plurality of flexible filaments may be made of a material such as aplastic, a metal, a shape memory metal, an alloy, a synthetic fiber, atextile fiber, or any combination thereof. Those skilled in the art willrecognize that a suitable material may be classified in more than onecategory. For example, a suitable material can be classified as both analloy and a shape memory metal. Any of the flexible filaments may bewound into yam for use. Additionally, the materials may be interwoven orinterlaced in any manner such as weaving, braiding or knitting.

The plurality of flexible filaments can contain more than one type offlexible filament. Further, the plurality of flexible filaments can beheterogeneously interwoven or interlaced. For example, the plurality offlexible filaments can be arranged to divide the cannula into segmentsalong any axis such that the segments contain flexible filaments ofdifferent materials, or the segments contain the same flexible filamentsarranged differently. For example, a cannula can be divided along itslength into three or more segments (e.g., a “proximal segment”, a“middle segment” and a “distal segment”). In this example, the proximalsegment of the cannula body can include textile fiber flexible filamentswhile the distal segment includes stainless steel flexible filaments inorder to provide stronger expansion force at the distal end. A cannulacan include any number of segments, or can be unsegmented.

The plurality of flexible filaments can have any shape such as, forexample, round, oval, flattened, triangular, rectangular, or anycombination thereof. The shape and thickness of the flexible filamentscan affect or influence the performance of the cannula. Additionally,the material of the flexible filament may also be spring-loaded ortorsioned to further allow the diameter of the lumen 5 to be varied.Specifically, when the material is altered, e.g., stretched,spring-loaded, deformed, activated, compressed, and/or torsioned, thediameter of the lumen 5 is decreased. The diameter of the lumen 5returns to its normal profile conformation (or to that of thesurrounding vessel) upon termination of the alteration.

The plurality of flexible filaments of the cannula body can be made ofone or more metals or alloys. Metals or alloys can provide a strongerexpansion force (e.g., hoop strength) relative to other materials of thesame size such as textile filaments. Because the diameter of metal oralloy flexible filaments can be smaller, while still achieving a certaindesired expansion force, a cannula including a plurality of flexiblefilaments made from metals or alloys can have larger lumens relative toother cannulas having a similar external diameter. Thus, whenconstructing smaller diameter cannulas, e.g., 1-mm diameter cannulas, itmay be preferable to use a plurality of metal flexible filaments such assurgical grade stainless steel. Those skilled in the art will recognizethat shape memory metals, such as nitinol, are also able to providestronger expansion force.

The plurality of flexible filaments can also be made of one or moresynthetic fibers. Suitable synthetic fibers include, but are not limitedto, rayon, acetate, polyester, nylon, acrylic, modacrylic, olefin,spandex and polypropylene, or combinations thereof.

Likewise, the plurality of flexible filaments can also be made of one ormore shape memory metals. The term “shape memory metals” relates tometals and metal alloys that can undergo a solid state phasetransformation from one crystal lattice structure to another crystallattice structure. Because the metal molecules remain in a closelypacked structure, the material remains in a solid state. The lowertemperature phase is called the Martensite phase and is characterized bythe shape memory metal being relatively soft and easily deformable. Thehigher temperature phase is called the Austenite phase and ischaracterized by the shape memory metal being relatively stronger. Thephase transformation between the Martensite phase and the Austenitephase occurs over a temperature range denoted by the nomenclature:

-   -   A_(s)=Austenite start temperature    -   A_(f)=Austenite finish temperature    -   M_(s)=Martensite start temperature    -   M_(f)=Martensite finish temperature

The temperature range of the phase transformation depends oncharacteristics such as the identity of the alloy and the relativecomposition. Altering these or other characteristics of the alloy canenhance operation of the cannula. For example, altering the processingof the shape memory metal can change the Austenite start temperature.

The molecular rearrangement of the crystal lattice structure results intwo different properties: shape memory effect and superelasticity. Theshape memory effect can occur when the shape memory metal is deformed inthe Martensite phase. Upon heating above the Austenite finishtemperature A_(f), the shape memory metal undergoes a phasetransformation into the Austenite phase, and assumes its originalconfiguration.

Shape memory metals also possess a quality known as superelasticity orpseudoelasticity. Superelasticity occurs to shape memory metalssubstantially composed of its Austenite form. When a force is imposed onthe shape memory metal, there is a phase transformation from theAustenite form to the Martensite form. When the load is decreased, theMartensite form transforms to the Austenite form.

Alloys with shape memory properties include, but are not limited to,nickel/titanium (also known as “nitinol”), copper/zinc/aluminum,copper/aluminum/nickel, silver/cadmium, gold/cadmium, copper/tin,copper/zinc, indium/titanium, nickel/aluminum, iron/platinum,manganese/copper, iron/manganese/silicon, and combinations thereof.

The shape memory and/or the superelastic properties of shape memorymetals can be used in the plurality of flexible filaments of thecannula. For example, a cannula comprising flexible filaments made fromone or more shape memory metals may be placed in it low profileconformation in the Martensite phase. Upon heating, either by bodytemperature or by an alternate heating source, the shape memory metalcan exist in the Austenite phase and assume the normal profileconformation. In this embodiment, shape memory metals preferably haveAustenite finish temperatures slightly less than body temperature. Forexample, the Austenite finish temperature can be between about 25° C.and 37° C., and preferably between 30° C. and 35° C. Similarly, in thisembodiment, the Austenite start temperature is preferably between roomtemperature and body temperature.

Similarly, in an alternative embodiment, a shape memory metal in theAustenite phase can be placed in the low profile conformation byapplying a stress to convert the metal to its Martensite phase. Afterthe cannula is properly placed or inserted, the stress can be relievedand the material of the cannula undergoes a phase transformation toreturn the cannula to its normal profile conformation in the Austenitephase.

The plurality of flexible filaments of the cannula body can alsocomprise one or more textile fibers, which include natural or syntheticfibers that can be interlaced to create textiles. Cannulas using textilefibers within the plurality of flexible filaments may be preferable forhigh-volume and low-cost production of high performance cannulas. Commontextile fiber-forming materials include, but are not limited to,cellulosics, e.g., linen, cotton, rayon and acetate; proteins, e.g.,wool and silk; polyamides; polyester; olefins; vinyls; acrylics;polytetrafluoroethylene; polyphenylene sulfide; aramids, e.g., Kevlar orNomex; and polyurethanes, e.g., Lycra, Pellethane and Biomer.

In order to manufacture some textile fibers, polymers can be extruded bytechniques such as wet, dry, or melt spinning. The resulting extrudedpolymer is then processed to obtain the desired texture, shape, andsize. By controlling morphology, textile fibers can be manufacturedhaving different mechanical properties. Additionally, the componentmaterials are unique in chemical structure and potential properties. Theproperties of the cannula can be altered by altering the shape of thetextile fiber, the identity of the textile fiber material, the use ofmonofilaments or multifilaments, the amount of twist binding the textilefibers together, the orientation of molecules in the textile fibers, andthe size of the textile fibers.

Flexible filaments used in the invention can be converted into yarnsusing any twisting or entangling processes that can enhance one or morecharacteristics. As used herein, the term “flexible filaments” alsorefers to flexible filament yarns. The plurality of flexible filamentscan be interlaced by various processes such as weaving, knitting andbraiding. Weaving the plurality of flexible filaments relates tointerlacing the plurality of flexible filaments at an angle. Forexample, weaving the plurality of flexible filaments can includeinterlacing the plurality of filaments at 90° angles. Knitting theplurality of flexible filaments relates to intermeshing loops of theplurality of flexible filaments. Knitted flexible filaments include weftor warp knit flexible filaments. Braiding the plurality of flexiblefilaments relates to crossing sets of flexible filaments in a diagonalpattern. Braided products can also include tubular structures, with orwithout a core, as well as ribbon.

Additionally, the woven, braided or knitted pluralities of flexiblefilaments can be modified to enhance one or more properties. Forexample, weft-knitted structures are highly extensible when comparedwith woven fabrics, but they are also dimensionally unstable unlessadditional yarns are used to interlock the loops and reduce theextension while increasing elastic recovery.

The cannula 6 may also comprise one or more mechanisms that allow thediameter of the lumen 5 to be varied. Such mechanisms may be, forexample, coils; springs; extensible, compressible, or releasable wings;foils; folds; and/or cages. However, one skilled in the art willrecognize that other suitable mechanisms may also be employed. Thecannula of the instant invention contains at least one mechanism that,upon actuation, serves to alter the cannula between a normal profileconformation and a low profile conformation. For example, whenactivated, the mechanism can place the cannula 6 in its low profileconformation, thereby decreasing the diameter of the lumen 5. Uponrelease of the mechanism, the cannula 6 will either return to its normalprofile conformation or expand to the diameter of the surrounding vesselor environment. Alternatively, the activated mechanism(s) can maintainthe cannula 6 in its normal profile conformation. Thus, in thisembodiment, upon release of the mechanism, the cannula 6 is placed inits low profile conformation, thereby decreasing the diameter of thelumen 5.

Suitable mechanisms for altering the diameter of the cannula of theinvention include, but are not limited to, a mandrel, an electric motor,a nano-engine, a change in pressurization, a wrapping string, a balloon,and a sheath. Those skilled in the art will recognize that thesemechanisms may be used alone, or in combination with any other suitablemechanism(s).

When the mechanism is a mandrel, the cannula is placed in its lowprofile conformation by inserting the mandrel into the lumen of thecannula. After the cannula is appropriately placed or inserted withinthe object to be cannulated, the mandrel may be removed, therebyallowing the cannula to return to its normal profile conformation.

The mechanism may also be a sheath surrounding the cannula. Thoseskilled in the art will recognize that keeping the length of the cannulaalmost constant during expansion of the cannula is one advantageassociated with compressing or collapsing the cannula from the outside.

Referring to FIG. 6A, the cannula 6 is placed in the low profileconformation by placing the cannula body 4 within a sheath 20. Thesheath may be any hollow structure that contains and maintains thecannula body 4 in the low profile conformation. For example, the sheathcan compress the cannula into its low profile conformation and canprovide a smooth outer surface for insertion and withdrawal of thecannula. The sheath can have any geometrical shape including circular,rectangular, oval, hexagonal, octagonal, and the like. The sheath mayhave a diameter less than the diameter of the cannula body 4 when in itsnormal profile conformation. Suitable materials for the construction ofthe sheath include, but are not limited to, polymers such aspolyvinylchloride, polyurethane, polyethylene, polypropylene,polyamides; metals; metal alloys; and combinations thereof. The sheathmay optionally contain holes and/or may be porous.

As shown in FIG. 6A, the cannula 6 is placed into its low profileconformation by compressing, or otherwise containing, the cannula body 4within the sheath 20. The cannula 6 may optionally have a means forsecuring the sheath 20 to the cannula body 4. The cannula 6 and sheath20 are inserted at a point of insertion and the distal end 3 of thecannula body 4 is placed in the appropriate position within the objectto be cannulated. Referring to FIG. 6B, the cannula 6 is returned to orplaced in its normal profile conformation by withdrawing the sheath 20proximally, as indicated by the arrow. As the sheath 20 is withdrawn,the distal end 3 of the cannula body 4 expands to the maximum diameterof the surrounding vessel or hollow organ, or to the maximum diameter ofthe cannula body 4 in the normal profile conformation. FIG. 6C shows thecannula 6 once returned to or placed in its normal profile conformation.Those skilled in the art will recognize that the sheath 20 may beremoved by any suitable means known in the art. For example, the sheath20 can be composed of a degradable or dissolvable material that breaksdown after insertion of the cannula 6 in the object to be cannulated.Once the sheath 20 fully degrades or dissolves, the cannula 6 will bereturned to its normal profile conformation.

The mechanism may also be a wrapping string. Referring to FIG. 7A, thecannula 6 is placed in the low profile conformation by wrapping awrapping string 30 around the cannula body 4. The cannula body 4 can bewrapped with a wrapping string 30 in any manner such as helically.Further, the wrapping string 30 can overlap, meet edge-to-edge, or havea gap between the loops of the string. In order to return the cannula tothe normal profile conformation, the wrapping string 30 is unwound,unwrapped or otherwise removed from the cannula body 4.

The cannula body 4 can be unwrapped in several ways. Referring to FIG.7B, the cannula body 4 can be unwrapped in a manner, such that thedistal end 32 of the wrapping string 30 remains wrapped around thecannula body 4 and advances towards the proximal end. (e.g., the distalend of the wrapping string is slid proximally) As shown in FIG. 7C, onlythe distal portion 32 of the wrapping string 30 remains on the proximalportion 1 of the cannula body 4.

Alternatively, the cannula body 4 can be wrapped in a manner such thatthe distal end 32 of the wrapping string 30 remains wrapped around thecannula body 4 and remains at the distal end 3 of the cannula body 4. Asthe cannula body 4 is unwrapped, the wrapping string 30 is removed fromthe proximal end 1 of the cannula body 4. When the cannula body 4 issubstantially unwrapped, only the distal portion 32 of the wrappingstring 30 remains on the proximal portion 1 of the cannula body 4following removal.

In yet another embodiment, the wrapping string is configured in such amanner as to unwrap from the distal portion 3 towards the proximalportion 1 of the cannula body 4. As the cannula body 4 is unwrapped, thewrapping string 30 is removed from the distal end 3 of the cannula body4. When the cannula body 4 is substantially unwrapped, only the proximalportion 32 of the wrapping string 30 remains on the proximal portion 1of the cannula body 4.

Those skilled in the art will recognize that other suitable means ofremoving the wrapping string may also be used. The wrapping string maycomprise one or more materials such as metal, plastic, synthetic fibersand biodegradable fibers. For example, the wrapping string can comprisea quickly degrading material such that the wrapping string degrades ordissolves after insertion. Additionally, the wrapping string can haveany width or thickness consistent with the scale of the object to becannulated.

The mechanism may also be a balloon. Referring to FIG. 8A, the cannulabody 4 is placed in the low profile conformation by inflating a balloon40, which exerts a force in the distal direction. As the balloon 40exerts the force, the cannula body changes from the normal profileconformation to the low profile conformation. Referring to FIG. 8B,after the cannula is positioned, the balloon 40 is collapsed and thecannula body 4 returns to the normal profile conformation.

Alternatively, the balloon 40 can be used to return the cannula to itsnormal profile conformation from the low profile conformation. Thecannula body 4 may be placed in the low profile conformation by theactuation of a suitable mechanism. The cannula body 4 is inserted at apoint of insertion. When the cannula body 4 is in the appropriatelocation, the balloon can be inflated in order to return the cannulabody to its normal profile conformation. After the cannula body isreturned to the normal profile conformation, the balloon may optionallybe deflated and removed from the cannula body. Alternatively, thedeflated balloon may remain within the lumen.

Those skilled in the art will recognize that the balloon can be anyshape as long as the shape allows the balloon to exert a force in thedirection necessary to alter the conformation of the cannula. Theballoon can be inserted into the object to be cannulated simultaneouslywith the cannula, or the balloon can be inserted into the lumen of thecannula after the cannula is positioned, or inserted, in the object tobe cannulated.

The conformation of the cannula can also be altered by changes inpressurization. For example, the cannula body 4 is placed in the lowprofile conformation by applying pressure in the distal direction. Asthe pressure exerts force in the distal direction, the cannula bodychanges from the normal profile conformation to the low profileconformation. After the cannula is placed or inserted, the pressure isdiscontinued or altered such that the cannula returns to the normalprofile conformation.

Alternatively, pressurization can be used to return the cannula to itsnormal profile conformation from the low profile conformation. Thecannula body 4 may be placed in the low profile conformation by theactuation of a suitable mechanism. The cannula body 4 is inserted at apoint of insertion. When the cannula body 4 is inserted in theappropriate location, pressure can be exerted in order to return thecannula body to its normal profile conformation. After the cannula bodyis returned to the normal profile conformation, the pressure may bediscontinued.

The mechanism may also include an electric motor or a nano-engine. Theelectric motor or nano-engine can be coupled to any suitable mechanismsuch as, for example, coils; springs; extensible, compressible, orreleasable wings; foils; folds; cages; mandrels; balloons; and a sheath.The electric motor or nano-engine can drive the mechanism, which altersthe cannula between its low profile conformation and its normal profileconformation. Similarly, the electric motor or nano-engine can becoupled to a device that exerts a force on the cannula to alter thecannula between its low profile conformation and its normal profileconformation. For example, the electric motor or nano-engine can becoupled to a fan that provides pressure that alters the conformation ofthe cannula.

High-performance cannulas according to the invention can have plasticproperties and/or elastic properties. Additionally, the cannula can besegmented into portions having plastic properties and other portionshaving elastic properties. As used herein, the term “elastic” relates tomaterials that deform in a recoverable way until a failure point isreached. Conversely, as used herein, the term “plastic” relates tomaterials that deform in a non-recoverable manner. A cannula cancomprise elastic materials, plastic materials or combinations thereof.Those skilled in the art will recognize that a cannula manufactured froma elastic material(s) can be deformed and will return to its originalconformation upon release. Alternatively, a cannula manufactured from aplastic material(s) will not return to its original conformation afterdeformation. The choice of elastic or plastic material(s) depends on thespecific desired function of a particular cannula. For example, aportion of a cannula can be made of a plastic material in order tosupport the surrounding vasculature, while the remaining portions may bemore elastic in nature.

Additionally, at least a portion of the material comprising the cannulabody 4 may be coated with a watertight coating. As illustrated in FIG.1C, a layer 14 of watertight coating is depicted on the surface ofcannula 6. For example, the watertight coating can be a plastic (such asplastic). However, those skilled in the relevant arts will recognizethat any suitable watertight coating may also be used. In oneembodiment, the layer 14 of watertight coating covers the entire cannulabody 4. Alternatively, in a separate embodiment, the layer 14 ofwatertight coating only covers the proximal end 1 of the cannula body 4,or only covers certain segments of the cannula body. For example, thecannula can be designed such that it contains alternating areas ofcoated and uncoated segments.

Also provided are cannulas having a dual lumen, which can be used tocarry two materials. For example, in hemodialysis, a dual lumen cannulacan be used such that the lumen of the first cannula body (i.e., “firstlumen”) can be used for suction (e.g., towards an artificial kidney) andthe lumen of the second cannula body (i.e., “second lumen”) can be usedfor reinjection (e.g., return of processed blood towards the patient) orvice versa.

The first and second cannula bodies can be positioned coaxially oradjacently. Referring to FIGS. 9 and 10, when the first and secondcannula bodies are positioned coaxially, a first cannula body 50, whichincludes a distal end 52 and a proximal end 54, surrounds a secondcannula body 60, which also includes a distal end 62 and a proximal end64. The distal end 62 of the second cannula body 60 can extend beyondthe distal end 52 of the first cannula body 50, or can remain within thefirst cannula body 50. The second cannula body 60 can be positionedanywhere within the lumen 56 of the first cannula body 50, i.e., thesecond cannula body 60 can be centered or offset within the lumen 56 ofthe first cannula body 50. The terms “first cannula” and “secondcannula” do not connote orientation. For example, the first cannula bodycan be the surrounding cannula body or the surrounded cannula body. Thefirst cannula and the second cannula may both be a cannula of thepresent invention or one may be a traditional cannula. Preferably, whenconfigured coaxially, the outer cannula is the cannula according to thepresent invention.

Alternatively, the dual lumens 56 and 66 can be located adjacentlyrather than coaxially. When located adjacently, the first cannula body50 and the second cannula body 60 can be the same or different diameterswhen in the normal profile conformation. Similarly, the lengths of thefirst cannula body 50 and the second cannula body 60 can be the same ordifferent, and the cannula bodies can be made of the same or differentmaterials.

When located adjacently, a portion of the first cannula body 50 can becoupled to a portion of the second cannula body 60 by any means known inthe art including, but not limited to, stitching, adhesive, solder,and/or mechanical coupling. Further, the first cannula body 50 can shareat least a portion of its body with the second cannula body 60. Thissharing can occur throughout the length of the cannula bodies,intermittently along a length of the cannula bodies, or a single spot onthe cannula bodies. Additionally, the first cannula body 50 and secondcannula body 60 can be arranged such that they are formed by a septumdividing two sides of a larger cannula body. In such an arrangement, thefirst cannula body is formed from a portion of the larger cannula bodyand one side of the septum while the second cannula body is formed fromanother portion of the larger cannula body and the other side of theseptum. Alternatively, there may be two septums within the largercannula body such that the first cannula body is formed from the largercannula body and one septum, and the second cannula is formed from thelarger cannula body and the other septum.

Further, the first septum can share a portion of its surface with thesecond septum. This sharing can occur throughout the length or width ofthe septums, intermittently along the length of the septums, or at asingle portion of a surface of each of the septums.

There are various methods of using the dual lumen cannulas describedherein. For example, a first cannula according to the invention can beplaced in its low profile conformation, inserted into the patient orobject to be cannulated and returned to its normal profile conformation.A second cannula according to the invention can then be placed insidethe first cannula to create two coaxial lumens. Alternatively, thesecond cannula is collapsed within the first cannula prior tocannulation. Both the first cannula and second cannula can be returnedto their normal profile conformation after insertion into the patient orthe object to be cannulized. Those skilled in the art will recognizethat the same or different mechanisms can be used to alter theconformation of the interior and exterior lumen.

Alternatively, a first cannula can be inserted into a patient and thelumen of the mandrel can be used as second lumen. The outer cannula canbe placed in its low-profile conformation and inserted into the patientor the object to be cannulized. Once properly positioned, the cannula isreturned to its normal profile conformation. The mandrel used to alterthe conformation of the cannula also contains a lumen. After returningthe outer cannula to the normal profile conformation, the mandrel iskept within the lumen of the cannula to create a coaxial dual lumen.

Any of the high performance cannulas described herein can also include aconnector on its proximal end. In FIG. 12A, a cannula 6 is illustratedwith connector 11. The connector 11 may be secured with a lockingmechanism 12 or a plug. One skilled in the art will recognize that theplug can comprise any shape or material suitable for securing theconnector. Alternatively, the connector 11 may be replaced by a flexible(silastic: e.g., 10 cm.) tube, which allows for clamping of the cannula(at the level of the flexible tube) without damage. Additionally, a usercould select a connector in accordance with the diameter of the linetubing utilized (cannula-connector line). The proximal end of thecannula may additionally (or alternatively) contain a connecting sleeverather than a connector. The connecting sleeve can couple the cannula toa perfusion system or other device. The connecting sleeve can compriseany shape, size or material suitable for coupling the cannula to anexternal device. Additionally, the connecting sleeve may be configuredto couple a cannula with a device, wherein the cannula and device have adifferent diameter, cross-sectional width, and/or size.

According to another embodiment of the invention, a mandrel may bemounted on a porous plug. The porous plug permits the passage of airnecessary for venting the cannula. In one implementation, the mandrel ishollow and may be mounted in the porous plug. The porous plug mayfurther be perforated so as to allow a guidewire (passing through thecannula tip and into the mandrel) to exit therethrough. The porous plug,together with the mandrel, preferably fits snugly into the flexible tube(used in place of the connector, as described above) at the cannula end.Hence, the cannula may be collapsed with the plug-carrying mandrel, andmay further remain in this configuration due to the snug fit of theporous plug in the flexible tube.

The cannulas of the invention can also include one or more additionaldevices to increase the functionality and/or performance of the cannula.For example, the cannula can include one or more microturbines, whichcan provide enhanced capabilities such as increasing the flow rate offluids through the cannula. The cannulas of the invention may alsoinclude one or more sensors, which can be coupled to various portions ofthe cannula to enhance performance or functionality. Sensors coupled toone or more microturbines can be used to adjust and/or maintain theoutput of the turbine. Similarly, sensors can be coupled to any suitablemechanism that can be used to change or alter the diameter of the lumen.For example, the cannula can include sensors coupled to small electricmotors to facilitate telemanipulation of the cannula.

The cannulas according to the invention are characterized by a high rateof fluid flow through the lumen 5. Specifically, the rate of fluid flowthrough the lumen 5 is between 1 mL/min and 100 L/min. Preferably, therate of fluid flow is between about 100 mL/min and about 6 L/min. Whenused in connection with cardiac surgery, typical fluid flow ratesthrough the cannula 6 are between about 100 mL/min and 6 L/min. Whenused during dialysis, or hemofiltration, typical fluid flow ratesthrough the cannula 6 are between about 100 mL/min and about 500 mL/min.When used for intravenous delivery of fluids, typical fluid flow ratesthrough the cannula are between about 1 mL/min and about 10 mL/min. Thusthose skilled in the art will recognize that the use of the cannulasaccording to the invention is desirable for any application where acontinuous fluid flow is required.

The cannulas according to the invention can be a variety of sizes. Forexample, they can be miniaturized for use in the cannulation of smallvessels or objects. Alternatively, they can be enlarged for cannulationof larger vessels or objects. Those skilled in the art will be able toroutinely select an appropriate sized cannula.

Method of Using High Performance Cannulas

The invention also provides methods for using the high performancecannulas according to the invention. For example, the cannula 6 can beplaced in its low profile conformation, inserted into the object to becannulated, and returned to its normal profile conformation. In someembodiments, in the normal profile conformation, the cannula 6 returnsto its original shape and diameter distal to the point of insertion 2.In other embodiments in the normal profile conformation, the cannula 6expands up to the internal diameter of the surrounding vessel orenvironment distal to the point of insertion 2. When used according tothese methods, the cannulas of the invention result in a smaller accessaperture than other traditional cannulas that are commonly used forcannulation. Advantageously, this smaller access aperture does notadversely impact the flow rate of fluids through the cannula 6.

When used according to the methods of the invention, the conformation ofthe cannulas 6 of the invention can be altered before, during, and/orafter cannulation.

Cannulas according to the instant invention can be used in a variety ofmedical and non-medical contexts. For example, the methods outlinedabove can be used for percutaneous insertion, central cannulation,tracheal tubes, chest tubes, drainage catheters, heart surgery, anddialysis as well as in any non-medical or extramedical situations orapplications in which a continuous fluid flow and a small accessaperture are desirable. Those of ordinary skill will recognize that thecannulas according to the invention will be suitable for a variety ofpurposes where a minimally invasive means of obtaining a continuous flowof fluids is desired.

Because of the ability to decrease the diameter of the lumen 5 of thecannula 6 at the point of insertion 2 without impacting the flow rate offluids through the cannulas, the cannulas according to the invention areparticularly suitable for use in minimally invasive procedures (in bothmedical and non-medical contexts) and/or surgeries. By way ofnon-limiting example, the cannulas of the invention can be used forblood gas measurement and for establishing a continuous shunt.

The cannulas according to the invention may be included as a part of ahigh performance cannulation kit. For example, the kit may include asharp hollow needle, a J-type guidewire 8, a set of dilators, a mandrel7 having a locking mechanism 12, and the high performance cannulas ofthe instant invention packaged together. Those skilled in the relevantarts will recognize that kits comprising additional elements can also beused.

Medical Uses

The high-performance cannulas of the invention can be used in a varietyof medical uses and contexts. Those skilled in the art will recognizethat the high performance cannulas described herein can be used forinsertion into any hollow organ such, as a vein, an artery, a urethra, aureter, an intestine, an esophagus, a trachea, a bronchial tube, apleural space, and a peritoneum. As used herein, the term “hollow organ”refers to any structure containing a lumen, and can include vesselswithin solid organs such as kidneys. Further, the cannula can beinserted through an orifice and/or through an incision in the skin.

Arterial Cannulas

One advantage provided by a self-expanding venous cannula (which may becollapsed to a lower profile prior to insertion), is an increase in thevolume of blood flow through the cannula coupled with a decreasedpressure drop, and a decrease in shear stress. These characteristics arealso of interest for efficient blood return via an arterial cannula,which can change its shape once positioned in situ. For a given accessaperture on the arterial side, an application of the high flow cannuladesign described herein (i.e., collapsed insertion and self-expansion insitu) has, in addition to a decreased pressure drop, the additionaladvantage of diminishing the velocity of the blood jet at the cannulaoutlet. This reduces the danger of high-velocity jet-lesions of theaortic wall, as well as the potential for aortic wall plaquemobilization and secondary embolization.

Access to the Veins and Arteries

Access catheters are generally necessary for transfusion of fluids,plasma-expanders, blood components or substitutes, and/or for takingmeasurements. Typical applications include massive volume infusions forpatients in circulatory collapse (shock). Under such circumstances, theperipheral target vessels are usually collapsed (e.g., empty due to alack of circulating blood) and constricted (e.g., due to low cardiacoutput, centralization, and/or high levels of circulatingvaso-constricting agents). Thus, puncturing such collapsed and/orconstricted small access vessels may be difficult. Hence, small-borecatheters are usually preferred.

However, one drawback associated with the use of small-bore catheters isthat their small luminal diameter may serve to limit flow through thecatheter. As such, large-volume transfusions over a short time periodmay be difficult and/or prolonged, and this may be detrimental for apatient.

To remedy this and/or other drawbacks associated with the use ofsmall-bore catheters, high flow access catheters based on the high flowcannula design described herein (e.g., collapsed insertion andself-expansion in situ) may be used. Specifically, the high flow accesscatheter may comprise a flexible, elastic plastic catheter that can bestretched over a hollow mandrel in order to be made thinner forintroduction over a guide-wire. Upon removal of the mandrel, thecatheter will expand to its initial diameter, which may be larger thanthe diameter at the point of insertion. In some embodiments, the lumenof the catheter may be enlarged (e.g., expanded) over its entire length(either fully or in part).

The high flow access catheter may be stretched over acentrally-positioned mandrel in a number of ways. For instance, thediameter of the tip orifice of the catheter may be smaller than thediameter of the mandrel. Alternatively, other mechanisms (e.g., bars,cams, hooks, etc.) may be used to keep the mandrel within the desiredposition of the tip of the catheter during loading and insertion.Examples of such mechanisms may include, but are not limited to: (1) aconically shaped tip with central and lateral holes; (2) a two-or-morestage design with or without lateral holes; (3) a tapered design withlateral slits that open when the catheter is expanded or pressurized;and (4) a flexible grid design similar to the one described for the highflow cannulas.

Any suitable mechanisms that allow for increased cross-sectional area ofthe catheter following insertion may be employed. Such mechanisms mayinclude, but are not limited to, foils, springs, coils, folds or othersuitable mechanisms, and those skilled in the art will routinely be ableto select a suitable mechanism. Any designs and/or mechanisms, which aidin establishing a shorter, narrow path once the catheter (or cannula) isin its expanded, inserted position may result in higher fluid transferrates through the catheter (or cannula).

Hemofiltration/Dialysis

The cannulas and access catheters described herein may also be modifiedfor use in hemofiltration and dialysis. During hemofiltration anddialysis, efficient blood purification is mainly limited by the volumeof blood flow that can be achieved. In contrast to the access situationfor rapid transfusion, where one main goal is to enable transfer of ahigh volume of blood to the patient within a short time frame,hemofiltration and dialysis typically require two lines: (1) one forblood withdrawal; and (2) one for blood return. Small bore catheterstend to limit flow more on the blood-collecting side where negativepressure is usually required to increase flow (e.g., risk of donorvessel and/or line collapse) as opposed to the arterial side, whereinthe positive pressure used helps to keep the line and the recipientvessel open.

Two high performance cannula-type catheters designed for collapsedinsertion and expansion in situ can be used. For example, the dual lumencannulas described herein may be used. In certain embodiments, a coaxialdesign having only one vessel puncture for blood drainage and return maybe used. However, those skilled in the art will also recognize that thetwo catheters may be positioned adjacently. Various design options alsoexist for coaxial dual-lumen catheters which may be collapsed forinsertion, including, for example, a dual-lumen catheter comprised oftwo collapsible catheters, one within the other. In one embodiment, theinner lumen (which may be used for returning the blood and may thereforehave a positive pressure load) may be made of soft, collapsible flexiblematerial. Such a material may have little or no ability to self-expand.Blood may serve to unfold the inner lumen as it is pumped through theinner lumen. Blood may drain through the outer lumen and return throughthe inner lumen, or vice versa, according to various embodiments.

Alternatively, two separate catheters may be provided. A first, basicself-expandable venous catheter may be used for collecting blood, and asecond, return catheter may be inserted in a coaxial position, ratherthan using a mandrel for stretching the cannula. The latter design mayemploy a special manifold that enables the separation of the two bloodflows (peripheral versus central), to connect them to the tubing flowingtoward and away from the pump, respectively.

Trachea (Transoral, Transnasal)

The high flow cannula principles and embodiments described herein mayalso be applied to tracheal intubations. Advantages associated with thisuse include, but are not limited to: (1) providing one self-expandingtube that can fit several sizes; (2) enabling a self-expanding cannulato expand to the optimal diameter for a given trachea; (3) enablingsuperior intraluminal air flow by freeing up the space that is typicallyoccupied by balloons in associated with known procedures; (4) enablingthe portion of the self-expanding tube sitting within the trachea to beuncovered, thus allowing for spontaneous ciliary motion and mucustransportation in this area; and (5) enabling the self-expandingtracheal tube to be inserted over a guide wire.

Stretching the tube over a hollow mandrel may be required to collapsethe self-expanding tube prior to insertion into a trachea.

In contrast to the self-expanding cannula wherein the presence of aconical tip may not impede blood flows, both ends of a tracheal tubeshould remain open as widely as possible to allow for an optimalbronchial opening. To achieve this, the wires (or plurality of flexiblefilaments) of the grid structure of the tracheal cannula (or expandingtracheal tube) may form a loop at the tracheal end of the tube. Thesewires can be captured by hooks or filaments, etc., and can be kept closeto the tip of the mandrel (covered by a cap if necessary) duringinsertion of the tracheal tube.

Tracheotomy

The technology outlined above for a high flow inter-tracheal tube mayalso be applied for tracheotomy tubes. The dimensions of the high-flowinter-tracheal tube may be adapted for such an application, and the tipfor the collapsed condition may be modified for percutaneous insertionover a guide-wire following dilation with serial dilators.

Non-Medical Uses

Those skilled in the art will recognize that the cannulas of theinvention can be used in many non-medical applications involvingtransporting materials such as fluids, powders and gases through pipesor tubes, which often have a fixed diameter resulting from a specificaccess aperture configuration. In such a situations, a traditionalapproach to filling or emptying a tank (or other vessel) is selecting apipe or tube having a diameter equal to or less than the diameter of theaccess orifice. Although tubing with a relatively small cross sectionalarea compared with its length results in a significant pressure drop,the use of more powerful pumps usually addresses the resulting flowlimitation. This approach tends to be effective when using positivepressure, because the maximum pressure is primarily limited by thestrength of the tubing wall and of the media to be transported.

However, when using negative pressure, other considerations must betaken into account. First, some fluids are not resistant to negativepressures (e.g., vaporization, loss of biological activity, etc).Second, the maximum negative pressure is limited. Consequently, pressuredrops resulting from a small cross sectional area, which in turn is afunction of a small access orifice, is more of an issue.

The use of the cannulas of the invention (e.g., cannulas with collapsedinsertion and in situ expansion) provides significant advantages in manytechnical applications where a short narrowing of a path for fluids orother media allows for significantly higher flows in comparison tolonger narrow paths.

The cannulas of the invention can be used to fill and empty (through anarrow orifice) mobile tanks such as those found in, for example, cars,trucks, ships, planes, tanker-planes and other vehicles. For example, acannula of the appropriate size can be placed in the low profileconformation and inserted into the tank. The cannula can then bereturned to its normal profile conformation and the tank can be filledor emptied.

The cannula can also be used to fill or empty fluids, or mediaexhibiting fluid-like behavior, from fixed tanks such caverns or silos.Examples of fluids, or media exhibiting fluid-like behavior include, butare not limited to water, gasoline, kerosene, fuel, crude, vapor, gases,powder, grains, rice, beans, and the like.

The characteristics of the specific cannula used in non-medical contextscan vary depending on the object to be cannulated. Those skilled in theart will recognize that, for industrial applications, the diameter ofthe cannula in its normal profile conformation can be very wide.Similarly, the cannulas can be made of stronger and more durable,flexible materials.

Emptying a tank from the top through a narrow access aperture requires atube passing through the narrow access to the bottom of the tank.Consequently, the expanding portion of the cannula within the tankshould be tightly covered over a substantial portion of the lengthwithin the tank. However, it is not necessary for the cover to couple orattach directly to the tube body, which can be any type of expandablescaffold or grid that provides a lumen. In negative pressureapplications, the cover can be loosely coupled to the expandablescaffold such that the resulting suction draws the cover onto thescaffold and draws the liquid through the tube from the open end. Inpositive pressure applications, once the cover is appropriatelypositioned, the scaffold can optionally be removed, as the pressurizedfluid will maintain the cover.

Methods of Making High Performance Cannulas

Cannulas can be manufactured by a variety of methods. For example, theplurality of flexible filaments of the cannula body can be interlaced orinterwoven by weaving, braiding or knitting. One skilled in the art willrecognize the various automated and non-automated methods forinterlacing or interweaving can be employed. The resulting interlacedplurality of flexible filaments can form, for example, a grid- ormesh-like structure that can have its diameter varied.

Alternatively, a similar grid- or mesh-like configuration of a pluralityof flexible filaments may be made by etching, cutting or otherwiseremoving portions of a continuous open-ended body, e.g., a tubular body.For example, the continuous body may comprise materials such as plastic,metal and shape memory metal. Portions of a continuous tube can beremoved, by laser-cutting or water-cutting the tube, to create theappropriate grid-like structure. The resulting plastic cannula isexpandable to a larger diameter (compared to the diameter in its lowprofile conformation) in situ.

Alternatively, the cannula can be manufactured by injection molding. Thematerials comprising the plurality of flexible filaments are liquefiedby heating, chemical means or other means, and injected into a suitablemolding. Similarly, the cannula body can be manufactured by extrusion.Any of the above manufacturing processes can be combined to create asuitable cannula.

To accelerate the manufacturing process, a photo-activated material maybe used for potting the wires or filaments of the grid at a tip of thecannula. For example, the flexible filaments may be potted at the distalend of the cannula with a photo-activated epoxy, which works faster thanother potting materials.

The invention will be further described in the following examples, whichdo not limit the scope of the invention described in the claims.

EXAMPLE 1 In Vivo Cannula Comparisons

In vivo experiments in bovine were conducted to compare the flow rate offluids through the high performance cannula 6 of the invention and othercommercially available cannulas of various diameters. Specifically, thecomparisons involved the cannulation of the superior vena cava (thetarget vessel) through the jugular vein (the access vessel) aftercalibration of the aperture (through which the cannula and blood flowhave to pass) access to 28 French (9.33 mm), 24 French (8 mm), and 20French (6.66 mm) cannulas. The cannulas tested included DLP cannulas(Medtronic), Biomedicus cannulas (Medtronic), generic chest tubecannulas, and the high performance cannulas according to the instantinvention. To insure standardized conditioning, gravity drainage was setat 60 cm of water for each of the cannulas tested.

The results of the comparisons are shown in Table 1. TABLE 1 ComparisonA Comparison B Comparison C 28 French 24 French 20 French (9.33 mm) (8mm) (6.66 mm) Y SD N Y SD N Y SD N DLP cannulas 4.117 0.076 3 3.3170.076 3 1.733 0.153 3 Biomedicus 3.983 0.046 3 3.930 0.036 3 2.670 0.0703 cannulas Chest tube 3.603 0.055 3 2.947 0.117 3 2.210 0.046 3 High5.350 0.132 3 5.217 0.076 3 4.173 0.087 3 performance cannulas

The results depicted in Table 1 demonstrate the flow rate of fluids (Y)in L/min through each of the cannulas tested. The results also show thestandard deviation (SD) and number tested (N) for each cannula. For alltested, clinically-relevant cannula diameters (i.e., 28 French, 24French, and 20 French), the high performance cannulas described hereinprovided the best flow rate results. The flow rate of fluids through thehigh performance cannulas was 33-60% higher than the flow rate throughthe other commonly used, commercially available cannulas. Specifically,for the 20 French outflow vessel, the flow rate with the highperformance cannula was superior to the flow rate for the best 28 Frenchcannula (4.117 L/min vs. 4.173 L/min).

Thus, these results demonstrated that the high performance cannulasaccording to the instant invention are superior to the cannulas commonlyused by those skilled in the art. These results provided proof of theprinciple that the flow rate usually generated with a 28 French cannulacan also be provided by a high performance cannula requiring only a 20French hole. The results of these in vivo comparisons are also shown inFIG. 12.

EXAMPLE 2 Use of High Performance Cannulas

In order to prepare the high performance cannula 6 for use, a mandrel 7(as shown, for example, in FIG. 3A) is introduced into the cannula 6.Next the cannula 6 is stretched over the mandrel 7 in order to reduceits diameter. Once the cannula 6 is fully in its low profileconformation, it will have a minimal outer diameter.

The vessel to be cannulated is then punctured with the sharp hollowneedle. A J-tip guidewire 8 is then introduced into the vessel. Properpositioning of the guidewire is checked by ultrasound, fluoroscopy, orany other suitable means. While keeping the guidewire in place in situ,the needle is then removed from the vessel.

To achieve vessel orifice (e.g., access aperture) dilation, a small(e.g., No. 1) dilator is placed over the guidewire 8 and then removed,while the guidewire 8 remains in place. The access aperture can beredilated using an intermediate (No. 2) dilator that is inserted andremoved. Finally, the largest dilator (No. 3) is inserted and removed.

While insuring that the guidewire 8 remains in the proper position, thefully stretched (e.g., low profile conformation) and locked highperformance cannula 6 is loaded onto the guidewire 8. This isaccomplished by passing the guidewire 8 through the central hole 9 atthe tip 10 of the cannula 6 and through the central hole at the tip ofthe mandrel 7. The cannula 6 is inserted over the wire through thepredilated hole in the vessel at the target site.

Once the mandrel 7 is unlocked, the cannula 6 can be pulled back at anytime. However, for further advancement, reloading of the cannula 6 ontothe mandrel 7 may be necessary. After the mandrel 7 is unlocked, thehigh performance cannula 6 will expand in situ. Prior to completeremoval of the mandrel 7, the position of the cannula 6 should bechecked and monitored.

Once an adequate cannula position is reached, the high performancecannula 6 may be secured and the mandrel 7 removed. Finally, the securedhigh performance cannula 6 can be connected to a line. A mandrel 7 maybe used for repositioning, as necessary.

EXAMPLE 3 Manufacture of High Performance Cannulas

The manufacture of the high performance cannulas may include some or allof the following steps: (a) defining the diameter and length needed; (b)selecting the appropriate materials; (c) preparing the cannula 6; (d)preparing the mandrel 7; and (e) preparing a locking mechanism 12.Additionally, those skilled in the relevant arts will recognize that thehigh performance cannulas of the invention may also be made by any othermethods or processes known in the art.

A variety of parameters influence and define the optimal diameter andlength configuration of the high performance cannulas of the invention.These parameters include target flow, target vessel diameter, targetvessel length, target vessel access diameter, target vessel accesslength, desired covered cannula 6 length proximal to the point ofinsertion, and/or the desired connector. In one embodiment the cannula 6can be approximately ⅜″ in diameter and 50-70 cm in length, depending onthe particular application. Determination of the appropriate diameterand length is within the routine skill of those in the art.

Suitable materials for manufacturing the high performance cannulas canbe categorized as cannula size-independent materials and cannulasize-dependent materials. Size-independent materials may include, butare not limited to, medical grade polyurethanes (used for potting thecannula tip 10), medical grade silicones (used for covering the portionof the cannula 6 close to the connector 11), and medical grade plasticseparating agents. The cannula lumen 5 may contain a spacer thatfunctions to maintain a hole for the guidewire 8 in the potted cannulatip 10.

Cannula size-dependent materials include the interlaced self-expandingwires and/or a plurality of flexible filaments that comprise the cannulabody 4. The wires can be made of, for example, a medical grade stainlesssteel coated with a plastic. Alternatively, an elastic honeycombstructure, a grid, lasercut nitinol, or a plastic scaffold may be used.Other cannula size-dependent materials include molds for potting thecannula tip 10, the connector 11, the mandrel 7, and the lockingmechanism 12.

The high performance cannulas 6 of the invention can be made withadditional working length at both ends of the final cannula 6dimensions. The interlaced wire bundle at the distal end 3 of thecannula 6 is tied together to a minimal diameter after the insertion ofa central spacer wire, which has been treated with a separate form ofthe potting material. Any excess length can then be removed.

Using a mold prepared with a separating agent, the cannula tip 10 ispositioned within the mold. A polyurethane used for potting is mixed,centrifuged, and potted on the cannula tip 10. Following polymerizationand unmolding, the spacer is removed, thereby providing a path for theguidewire 8. The tip may be potted using a photoactivated epoxy.Finally, the cannula tip 10 is cut and polished.

Next, the proximal end 1 of the cannula 6 can be coated. Usingpositioning tools, a partial length dip coating of the proximal end 1 isperformed. This dip coating can be a medical grade silicone or any othersuitable coating. This coating is then polymerized, and severaladditional layers can be added. Finally, the proximal end 1 of thecannula 6 can be mounted with an appropriate connector 11. Alternatively(or additionally), various segments of the cannula may be coated (i.e.,in an alternating fashion).

In order to prepare the mandrel 7, an adequate diameter of Teflon (orany other flexible (i.e., plastic) rod having a conical tip and acentral lumen for the guidewire 8, is used. The length of this rod isthen adapted for the length of the high performance cannula 6 to beused.

Finally, the locking mechanism 12 is made by selecting an adequate capwith a locking mechanism that is assembled with the cannula 6. Careshould be taken to select a locking mechanism 12 of proper length forthe selected high performance cannula 6. An example of an appropriatelocking mechanism 12 is illustrated in FIGS. 12A-12C. Alternatively, theconnector is capped with a plug. When connecting the cannula to a devicesuch as a perfusion machine, a connecting sleeve is used in place of theconnector and locking mechanism. A sleeve capable of coupling thecannula to the machine is selected and placed over the proximal end ofthe cannula.

Other Embodiments

While the invention has been described in conjunction with the detaileddescription thereof, the foregoing description is intended to illustrateand not limit the scope of the invention, which is defined by the scopeof the appended claims. Other aspects, advantages, and modifications arewithin the scope of the following claims. It will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention encompassed bythe appended claims.

1. A cannula adapted for insertion at a point of insertion, the cannulacomprising: a cannula body having a proximal end, a distal end, and alumen extending between the proximal and distal ends, the lumen having adiameter, the cannula body comprising a plurality of flexible filamentsthat allow the diameter of the lumen to be varied, wherein the distalend optionally further comprises a tip, wherein the tip is removable oreccentrically located; at least one mechanism that, upon actuation,serves to alter the conformation of the cannula between a normal profileconformation and a low profile conformation, wherein the mechanism isselected from the group consisting of a mandrel, an electric motor, achange in pressurization, a wrapping string, a balloon and a sheath;wherein, when the cannula is in use, the normal profile conformation ischaracterized by the cannula having a lumen diameter at the point ofinsertion which is smaller than the lumen diameter both proximal anddistal to the point of insertion, wherein the lumen diameter distal tothe point of insertion is expandable up to the diameter of a surroundingvessel or to the maximum lumen diameter; and wherein the low profileconformation is characterized by the cannula having a lumen diameter atthe point of insertion that is greater than the lumen diameter distal tothe point of insertion.
 2. The cannula of claim 1, wherein the pluralityof flexible filaments comprises one or more materials selected from thegroup consisting of metals, shape-memory metals, alloys, plastics,textile fibers, synthetic fibers, and combinations thereof.
 3. Thecannula of claim 1, wherein the plurality of flexible filaments have ashape selected from the group consisting of round, oval, flattened,triangular, rectangular and combinations thereof.
 4. The cannula ofclaim 2, wherein the metal is stainless steel.
 5. The cannula of claim1, wherein the plurality of flexible filaments are textile fibers. 6.The cannula of claim 1, wherein the plurality of flexible filaments arebraided together.
 7. The cannula of claim 1, wherein the plurality offlexible filaments are knitted together.
 8. The cannula of claim 1,wherein the plurality of flexible filaments are interwoven.
 9. Thecannula of claim 1, wherein the plurality of flexible filaments areinterlaced.
 10. The cannula of claim 1, wherein the cannula is insertedinto hollow organ.
 11. The cannula of claim 10, wherein the hollow organis selected from the group consisting of a vein, an artery, a urethra, aureter, an intestine, an esophagus, a trachea, a bronchial tube, apleural space, and a peritoneum.
 12. The cannula of claim 1, wherein thecannula is in its normal profile conformation when in use and whereinthe lumen diameter distal to the point of insertion varies in relationto the diameter of the surrounding vessel.
 13. The cannula of claim 1,wherein the cannula is in its normal profile conformation when in useand wherein the portion of the cannula distal to the point of insertionsupports an inner surface of the surrounding vessel.
 14. The cannula ofclaim 1, wherein the plurality of flexible filaments are elastic. 15.The cannula of claim 1, wherein the plurality of flexible filaments areplastic.
 16. The cannula of claim 1, wherein at least a portion of thecannula is coated with a water-tight coating.
 17. The cannula of claim16, wherein the water-tight coating is plastic.
 18. The cannula of claim1, wherein the cannula tip comprises a photoactivated epoxy.
 19. Thecannula of claim 1, further comprising a connecting sleeve.
 20. Thecannula of claim 1, wherein the flow rate of fluid through the cannulais less than about 150 mL/min.
 21. The cannula of claim 1, wherein theflow rate of fluid through the cannula is between about 1 mL/min andabout 10 mL/min.
 22. A method for using the cannula of claim 1 in amedical context, the method comprising: placing the cannula in its lowprofile conformation; inserting the cannula into a hollow organ of apatient at a point of insertion; and returning the cannula to its normalprofile conformation, wherein in the normal profile conformation, thecannula expands distal to the point of insertion up to the diameter ofthe hollow organ or to the maximum diameter of the lumen.
 23. The methodof claim 22, wherein, when the cannula is in the normal profileconformation, the diameter of the cannula distal to the point ofinsertion varies in relation to the diameter of the hollow organ. 24.The method of claim 22, wherein inserting the cannula into the holloworgan of the patient comprises inserting the cannula into a locationselected from the group consisting of the peritoneum, the trachea, thechest, the cardiovascular system, the kidneys, and the urinary system.25. The method of claim 24, wherein the hollow organ is selected fromthe group consisting of a vein, an artery, a urethra, a ureter, anintestine, an esophagus, a trachea, a bronchial tube, a pleural space,and a peritoneum.
 26. The method of claim 25 wherein the cannula isinserted into the trachea.
 27. The method of claim 26 wherein thecannula is inserted transorally, transnasally, or through a tracheotomy.28. The method of claim 22, wherein, when the cannula is used duringcardiac surgery, the flow rate of fluid through the cannula is betweenabout 100 mL/min and 6 L/min.
 29. The method of claim 22, wherein, whenthe cannula is used during dialysis or hemofiltration, the flow rate offluid through the cannula is between about 100 mL/min and 500 mL/min.30. The method of claim 22, wherein, when the cannula is used forintravenous delivery of fluids, the flow rate of fluid is between about1 mL/min and about 10 mL/min.
 31. A method for using the cannula ofclaim 1 in a non-medical context, the method comprising: placing thecannula in its low profile conformation; inserting the cannula into anobject to be cannulated selected from the group consisting of tubing, acontainer, a fluid-filled container, a powder-filled container, and agas-filled container; and returning the cannula to its normal profileconformation, wherein in the normal profile conformation, the cannulaexpands distal to the point of insertion up to the diameter of theobject or up to the maximum lumen diameter.
 32. A dual lumen cannulaadapted for insertion at a point of insertion for use in peritonealdialysis, hemodialysis or hemofiltration, the cannula comprising: afirst cannula body having a proximal end, a distal end, and a lumenextending between the proximal and distal ends, and a second cannulabody having a proximal end, a distal end, and a lumen extending betweenthe proximal and distal ends, the lumen of the first and second cannulabodies having a diameter, the first and second cannula bodies comprisinga plurality of flexible filaments that allow the diameter of the firstand second lumen to be varied, wherein the first and second distal endsoptionally further comprise a tip, wherein the tip is removable oreccentrically located; at least one mechanism that, upon actuation,serves to alter the conformation of the first cannula body, the secondcannula body, or both the first cannula body and the second cannulabody, between a normal profile conformation and a low profileconformation; wherein, when the dual lumen cannula is in use, the normalprofile conformation is characterized by the first and second cannulabodies having a lumen diameter at the point of insertion which issmaller than the lumen diameter both proximal and distal to the point ofinsertion, and wherein the lumen diameters of the first and secondcannula bodies distal to the point of insertion are expandable up to thediameter of a surrounding vessel or to the maximum lumen diameter; andwherein the low profile conformation is characterized by the first andsecond cannula bodies having a lumen diameter at the point of insertionthat is greater than the lumen diameter distal to the point ofinsertion.
 33. The dual lumen cannula of claim 32, wherein the pluralityof flexible filaments comprises one or more materials selected from thegroup consisting of metals, shape-memory metals, alloys, plastics,textile fibers, synthetic fibers, and combinations thereof.
 34. The duallumen cannula of claim 32, wherein the at least one mechanism isselected from the group consisting of a mandrel, an electric motor, achange in pressurization, a wrapping string, a balloon and a sheath. 35.The dual lumen cannula of claim 32, wherein the first and second cannulabodies are positioned coaxially.
 36. The dual lumen cannula of claim 32,wherein the first and second cannula bodies are positioned adjacently.37. A method for manufacturing the cannula of claim 1, wherein themethod is selected from the group consisting of injection molding,laser-cutting, water-cutting, extrusion and combinations thereof.